首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6209篇
  免费   425篇
  国内免费   776篇
林业   559篇
农学   548篇
基础科学   1047篇
  967篇
综合类   2468篇
农作物   106篇
水产渔业   589篇
畜牧兽医   770篇
园艺   68篇
植物保护   288篇
  2024年   43篇
  2023年   166篇
  2022年   247篇
  2021年   309篇
  2020年   255篇
  2019年   291篇
  2018年   189篇
  2017年   270篇
  2016年   296篇
  2015年   234篇
  2014年   304篇
  2013年   288篇
  2012年   411篇
  2011年   467篇
  2010年   388篇
  2009年   335篇
  2008年   334篇
  2007年   435篇
  2006年   377篇
  2005年   320篇
  2004年   244篇
  2003年   196篇
  2002年   150篇
  2001年   148篇
  2000年   99篇
  1999年   93篇
  1998年   94篇
  1997年   63篇
  1996年   65篇
  1995年   48篇
  1994年   46篇
  1993年   42篇
  1992年   35篇
  1991年   37篇
  1990年   25篇
  1989年   16篇
  1988年   15篇
  1987年   10篇
  1986年   14篇
  1985年   6篇
  1983年   2篇
  1982年   1篇
  1977年   1篇
  1956年   1篇
排序方式: 共有7410条查询结果,搜索用时 46 毫秒
91.
Based on the maximum flow principle about networks, a network flow approach to reliability evaluation in large scale netwerks ty mixing inereasing flow with decreasing flow is proposed in this paper.This approach gets the initial flow of each branch in a r.etwork associated with a state of the retwork by decreasing flows of some branches correlative to another state of the network.As a result, the number of flow compute required can be reduced enormously.The numerical example shows that the approach is powerful. The comparison of this approach with the minimal cutset one is also given in this paper.  相似文献   
92.
93.
94.
In order to upgrade traditional industry and realize the automation of furnace condition judgement and standardization of operation, an expert system for various furnace conditions and breakdown judgement and operation guidance on blast furnace are developed based on the theory of artificial intelligence and knowledge engineering. The system is fulfilled through C++Builder and combined with the actual production picture. The system has efficient and convenient man-machine interface by using menu operation method. The testing and operation of actual production data in simulation system indicate that the system is exact and reliable and can provide both the warning of various furnace breakdown and corresponding operation guidance.  相似文献   
95.
The idea for an expert system approach to the computer aided design of intelligent controllers (ESCAD1C) is discussed and the idea of two step modelling of an intelligent controller is presented on the basis of emulating human control behaviours to solve complex problems. The structure, functions and characteristics of ESCADTC system , and the design procedures of intelligent controllers are gived. The knowledge base and simulating functions for designing intelligent controllers are also described.  相似文献   
96.
Based on the model of Human Simulation Intelligent Controller (HSIC) presented briefly, a detailed algorithm was described for the servo system control by using the method of HSIC. Simulation results obtained proves the good performance of the control algorithm.  相似文献   
97.
This paper proposes an intelligent method for solving a kind of intractable combinatorial problems, investigates and analyzes several important problems of this kind Theoretical and experimental results show that this method is better than the classical backtracking method.  相似文献   
98.
Distribution Network Structure planning is a complex combinatorial optimization problem,which is difficult to solve properly by using traditional optimization methods.In order to solve this problem,Improved Immune Genetic Algorithm is introduced to the distribution network optimal planning. Improved Immune Genetic Algorithm draws into the immune diversity and antibody's density mechanism to maintain the individual's diversity and remains evolution algorithm's global stochastic searching ability,so it can promote diversity and the whole optimal-searching ability of genetic algorithm.The optimal module takes the minimum annual cost as its object,and the capacity and voltage drop of feeder and the radiation of distribution network as its restrictions.According to the require of radiation of distribution network,the spanning tree of the alternative network is taken as the initial solution to speed up the calculation.And the branch-exchange method is used in designing crossover operator and mutation operator to avoid the radiation checking and enhance the optimizing ability.This algorithm has been illustrated effectively by examples,at the same time,the calculation example demonstrates that,the algorithm has higher calculation speed than the traditional immune genetic algorithm.  相似文献   
99.
100.
An optimization approach for multi-relational joins based on the matching concept in graph theory is introduced. The basic idea lies in constructing a join graph from an expression of N-relation query, and seeking for a maximun matching with minimun total weight. The algorithm for bipartition(X, Y) is proposed in this paper.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号